A hybrid vehicle may include an engine and a motor that may be in mechanical communication. The motor may augment engine torque during conditions of high driver demand. The motor may also be used as sole propulsion force under certain conditions. The motor may also convert the vehicle's kinetic energy into electrical energy for use at a later time. Further, the motor may be used to start the engine when the engine is stopped. The engine may be started via the motor when the engine is warm or cold, and friction within the engine may change significantly between lower engine temperatures and higher engine temperatures. Consequently, the motor may need to supply additional torque to rotate the engine at lower temperatures. However, a battery supplying power to the motor may provide less charge at lower temperatures and it may discharge to some extent if the battery is not charged over a period of time. Therefore, it may be difficult to crank the engine at a repeatable speed during engine starting, and as a result, engine emissions may degrade.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for starting an engine, comprising: adjusting an engine cranking speed in response to battery power capability and an amount of power to crank an engine at a desired engine speed; and cranking the engine at the adjusted cranking speed.
By adjusting engine cranking speed in response to battery power capability and an amount of power to crank the engine at a desired engine speed, it may be possible to provide the technical result of lowering engine emissions and reducing engine controller calibration complexity. Further, the potential for a non-starting engine may also be reduced. For example, if a battery has less power capability to rotate an engine at a desired speed than the amount of power needed to rotate the engine at the desired speed, the engine cranking speed may be reduced to a lower speed where a fine-tuned engine starting calibration may be provided. Further, a predetermined number of engine cranking speeds may be established so that only a finite number of engine starting calibrations are used during engine starting. In this way, the engine may be started according to more limited starting conditions where an engine starting calibration may be more optimized.
The present description may provide several advantages. In particular, the approach may reduce engine starting emissions. Further, the approach may reduce the complexity of calibrating a controller for engine starting. Further still, the approach may improve engine starting over a wide range of engine operating conditions.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.